Enhancement of microstructure and initial permeability due to Cu substitution in Ni0.50-xCuxZn0.50Fe2O4 ferrites

Structural and magnetic properties of Cu substituted Ni0.50-xCuxZn0.50Fe2O4 ferrites (where x=0.0-0.25) prepared by an auto combustion method have been investigated. The X-ray diffraction patterns of these compositions confirmed the formation of the single phase spinel structure. The lattice parameter increases with the increase in Cu2+ content obeying Vegard's law. The particle size of the starting powder compositions varied from 22 to 72 nm. The theoretical density increases with increase in copper content whereas the Neel temperature decreases. The bulk density, grain size and permeability increases up to a certain level of Cu2+ substitution, beyond that all these properties decrease with increase in Cu2+ content. The bulk density increases with increase in sintering temperatures up to 1250 degrees C for the parent composition, while for substituted compositions it increases up to 1200 degrees C. Due to substitution of Cu2+, the real part of the initial permeability increases from 97 to similar to 390 for the sample sintered at 1100 degrees C and from 450 to 920 for the sample sintered at 1300 degrees C. The ferrites with higher initial permeability have a relatively lower resonance frequency, which obey Snoek's law. The initial permeability strongly depends on average grain size and intragranular porosity. The saturation magnetization, M-s, and the number of Bohr magneton, n(mu(B)), decreases up to x=0.15 due to the reduction of the A-B interaction in the AB(2)O(4) spinel type ferrites. Beyond that value of x, the M-s and the n(mu(B)) values are enhanced. The substitution of Cu2+ influences the magnetic parameters due to modification of the cation distribution. (C) 2011 Elsevier B.V. All rights reserved.